This invention relates to apparatus in which a slide member is selectively positioned by a turret, and is more particularly concerned with a frequency selector or tuner in which a variable reactance coupled to a slide member is adjusted by step-wise rotation of a turret.
In the frequency selector disclosed in U.S. Pat. No. 4,043,207, a slide member is moved to its maximum displacement, against the force of a spring, when an operating member is initially depressed, and then a turret is caused to rotate by further depressing the operating member. This mode of operation is required to prevent collision between the slide member and cooperating position setting elements on the turret, which would otherwise obstruct rotation of the turret and cause damage to the position setting elements and/or the slide member. Since the operating member must have a long stroke in order to provide, first, the maximum displacement of the slide member, and second, rotation of the turret, the size of the frequency selector must be great enough to accommodate the stroke, and the radio or other apparatus incorporating the frequency selector must be dimensioned accordingly. The operating knob provided at the end of the operating member projects greatly from the apparatus, which is undesirable from a design or safety standpoint, particularly when the apparatus is installed in a vehicle.
The frequency selector disclosed in the aforesaid patent has another disadvantage. In the construction disclosed, the slide member is resiliently brought into contact with position setting elements through a transmission rod provided on the slide member and urged toward the selected setting element by a strong spring, which resists a force applied to the slide member. Therefore, to rotate the turret, the operating knob must be depressed against a strong spring force, which is inconvenient.